Volvo 5.7 L Gsi 15 x 16 pitch 4 blade prop

[honduras74]

Hello everyone, I was wondering what your recommendation would be for a new prop. I have a 1999 Seasswirl 250 AFT with a Volvo 5.7 Gsi motor. The prop currently on it is a 4 blade 15/16 pitch aluminum. The problem I'm having is that the rpms do not go past 3000. It gives me around 26 Mph (gps) top on a fully loaded trip. If I'm alone it actually gets 200 rpms more. I am unable to get on plane if I have people on the boat with out the trim tabs. Would you guys please suggest what size 3 blade prop I could use to have the boat at proper rpms? Thanks.

 

[steelespike]

Is 3000 heavily loaded/ If 3000 is the max you reach you are 2000 short to make 5000. You can't do that with a prop.
A 16" pitch is slightly on the light side already.I suspect some sort of motor issue or perhaps a combination motor and boat problem.
Could be as simple as a throttle adjustment, perhaps a plug wire is off.perhaps the timing is off or not advancing as it should.
The boat may have a load of water stashed somewhere.Is the bottom clean and smooth?

 

[honduras74]

Bottom is clean newly painted. Hull is dry as a bone inside. Wires are good from resent full tune up. There is no hesitation or trembling on engine. I'll try checking the throttle adjustment. It's electronic ignition I will check it too. Wether loaded or not it tops out at.3k. Thanks

 

[Maclin]

If you just want to try a different prop, I would put a 3 blade 16p on it then compare. There may be something wrong with that prop you have. Trying a good/new known prop at that same pitch is worth a try in my book.

 

[MikDee]

IMO, I know it's a heavy boat, but I think your engine has lost some power along the way, It definitely needs to be checked out. You should be able to hit the specified WOT 4200-4600rpm with a 15"X17" 3blade prop. or, a 4 blade 15"X15" Just as an example: I had a 79'- 24' SeaRay cuddy with a 260hp Mercruiser that had a 15"X17" Black Max Alum prop that would reach 4600rpm @ 40mph. I'm guessing your later model SeaSwirl, maybe lighter, and the Volvo 5.7 is more powerful then my old 260 Merc. too.

 

[QC]

Check your tach before you do anything else. I am very suspicious of any boat that planes at all AND only reaches 3000 RPM. The engine condition does seem suspect, but need 100% accurate data to do anything, and I think it may be off.

 

[honduras74]

Ordered laser tachometer, will start there. I would have thought an extra blade made the engine work harder translating to a bigger pitch on a three blade i.e. 16 pitch 4 blade = 19 pitch 3 blade. One more thing, at 3000 rpms and Planing, fuel consumption is really great. Engine hums along giving me 95 miles from a 60 gallon tank with 4 guys and their required beer stock for the day. Thanks for your replies and suggestions.

 

[jestor68]

Dry weight is 5500 lbs. Add 600 lbs of people/stuff and 50 gal of gas, and the operating weight is about 6385.

The Mercury props selector indicates that it ought to do about 41 mph @ 4700 rpm using a 15/16 pitch 3 blade prop assuming a SX drive with a 1.43 gear ratio.

Something is off. I hope you haven't bought yourself a boat with a worn out motor. :faint2: